The World Health Organization wants tougher regulations on e-cigarettes, including stricter advertising regulations, a ban on indoor use, the withdrawal of fruit, candy and alcohol-based flavors, and health warnings on packets.

The Switzerland-based United Nations health body argued that vaping could be a threat to the health of adolescents and fetuses, writing that the vapor from e-cigarettes is "not merely water vapor as is often claimed in the marketing for these products" but "increases exposure of non-smokers and bystanders to nicotine and a number of toxicants."

The lack of firm data associating e-cigarettes with disease should not be a green light to vape, the W.H.O, argued. "Conclusive evidence about the association of [e-cigarettes] with diseases such as cancer will not be available for years or even decades," it said.

The W.H.O. estimated global e-cig sales of $3 billion in 2013, with around 466 brands and 7,764 flavors. Use of e-cigarettes, it says, doubled in North American and the European Union between 2008 and 2012.

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Marketing of the products came under particular attack in the report, which slammed e-cig ads for emulating tobacco marketing tactics like aligning with "celebrities, fashionable and youthful places and activities." Some e-cigs are marketed "as not only socially acceptable but as socially superior," the health organization complained. "Unsubstantiated or overstated claims of safety and cessation are frequent marketing themes."

Actor Mischa Barton is currently promoting Vapestick in the U.K., leading a search for Britain's most stylish vaper, while sites selling e-cigarettes, including Vapelondon.com and Ecigarettedirect.co.uk, regularly publish lists of "Top 10 celebrities who vape" including actors Leonardo DiCaprio, Johnny Depp, Lindsay Lohan, Robert Pattinson and Charlie Sheen.

In the United States, e-cigarette brand NJoy has run ads with the tagline, "Friends Don't Let Friends Smoke," and celebrities Jenny McCarthy and Stephen Dorff have appeared in campaigns for Lorillard's Blu e-cigarette.

The report calls for health warnings to be printed on e-cigarette packaging in the same way as traditional cigarettes, with such warnings to potentially include "potential nicotine addiction; potential respiratory, eyes, nose and throat irritant effect; and potential adverse effect on pregnancy."

The lack of evidence around health risks yet, and the potential for tobacco smokers to mitigate their harm by switching to electronic cigarettes, made even U.K. anti-smoking group Action on Smoking and Health wary of the W.H.O. report.

"ASH supports regulation of electronic cigarettes including controls on marketing but any regulation must be proportionate," said Hazel Cheeseman, director of policy and research at Action on Smoking and Health, in a statement. "Smoking kills 100,000 people in the UK alone. Smokers who switch to using electronic cigarettes in whole or in part are likely to substantially reduce their health risks. Although we cannot be sure that electronic cigarettes are completely safe, as the WHO acknowledges, they are considerably less harmful than smoking tobacco and research suggests that they are already helping smokers to quit."

"ASH does not support bringing electronic cigarettes under smokefree legislation as there is no evidence of any harm to bystanders from use of these devices," Ms. Cheeseman added.

The W.H.O. report also complained about the growing role of big tobacco in the e-cig business. Its recommendations will be debated at a World Health Organization conference in Moscow this October.